Knife for cutting in sliding contact with ruler edge

ABSTRACT

A knife having a knife blade with a cutting edge and a tip part of the cutting edge provided with a sliding flank face for sliding along a ruler edge as the tip part cuts a material lying below the ruler edge. The knife also has a guide member spaced apart from and in front of the tip part in the path of cutting advance thereof and having a sliding part for slidably contacting the material and a sliding face adapted to slide along the ruler edge and lying in the same plane as the sliding flank face of the blade, the guide member functioning to prevent the cutting edge from cutting into the ruler edge during a cutting operation.

United States Patent 1191 Himeno 1 1 June 17, 1975 [5 1 KNIFE FORCUTTING IN SLIDING 2,567,102 9/1951 Cook 30/335 x CONTACT WITH RULEREDGE 3,316,635 5/1967 Merrow et a1. 1 30/162 3,448,518 6/1969 Sklar30/162 [75] Inventor: Shohachi Himeno, Tokyo, apan 3,765,089 10/1973lbata 30/162 [73] Assignee: Conde Kabushiki Kaisha, Tokyo, FOREIGNPATENTS OR APPLICATIONS Japan 15,574 7/1905 United Kingdom 30/289 Dec.3, Japan [21] Appl. No.: 421,486

[30] Foreign Application Priority Data June 26, 1973 Japan 48-75863 [52]US. Cl. 30/162; 30/294; 30/320; 30/335; 30/336; 30/339 [5 I] Int. ClB26b 1/08 [58] Field of Search 30/162, 151, 294, 289, 30/286, 320, 335,336, 337, 339, 329

[ 56] References Cited UNITED STATES PATENTS 389,901 9/1888 Ridgely30/294 X 1,147,097 7/1915 Junior 1 30/289 X 1,211,777 1/1917 Stanfield30/294 1,250,538 12/1917 Williams 30/294 1,449,408 3/1923 Hull 30/162Primary Examiner-A1 Lawrence Smith Assistant Examiner-J. T. ZatargaAttorney, Agent, or Firm-Haseltine, Lake & Waters [57] ABSTRACT A knifehaving a knife blade with a cutting edge and a tip part of the cuttingedge provided with a sliding flank face for sliding along a ruler edgeas the tip part cuts a material lying below the ruler edge. The knifealso has a guide member spaced apart from and in front of the tip partin the path of cutting advance thereof and having a sliding part forslidably contacting the material and a sliding face adapted to slidealong the ruler edge and lying in the same plane as the sliding flankface of the blade, the guide member functioning to prevent the cuttingedge from cutting into the ruler edge during a cutting operation.

4 Claims, 19 Drawing Figures PATENTEDJUII 17 I975 SIIEU FIG. 8

FIG. 5 FIG. 6

FIG 9 FIG. IO

A I A WM w %/w b C A \MA Rf PATENTEDJUN 17 m5 SHEET PATENTEDJUN 17 I975SHEET O? i m ON W SN DON Q KNIFE FOR CUTTING IN SLIDING CONTACT WITHRULER EDGE BACKGROUND OF THE INVENTION This invention relates generallyto hand-held knives and more particularly to a knife to be moved alongand in slidinig contact with a guiding surface such as the guiding edgeof a ruler or straight edge or a drafting curve thereby to cut amaterial lying under the guiding surface.

In general, in the case where the cutting edge of a knife with asingle-beveled face is moved along a guiding -edge surface (hereinafterreferred to as a ruler edge), the flat, reverse flank face without abevel is placed against the ruler edge, while in the case of a knifewith double-beveled faces, one flank face of the knife tip is placedagainst the ruler edge. In either case, it is desirable that the sharpcutting edge tip be moved as it is held in close contact with the ruleredge in order to produce a cut line in the material being cut (e.g., asheet of a paper) which conforms accurately with the ruler edge.

This is difficult, however, for the following reasons. A knife for thepurpose referred to above ordinarily has a hilt or handle part which ismarkedly larger than the cutting edge, and this grip part is held byhand and pulled or pushed to cause the cutting edge cut into thematerial to be cut. For this reason, it is difficult even for aconsiderably skilled person to move the cutting edge tip along the ruleredge as the tip is kept positively in continual and positive contactwith the ruler edge. If the cutting edge tip should deviate inward evenslightly from its true course, that is, toward the direction for cuttinginto the ruler, it would thus cut into the ruler edge. On the otherhand, if the pressure for keeping the cutting edge firmly against theruler edge is relaxed out of fear of this cutting into the ruler, thecutting edge tip will tend to separate from the ruler edge, whereby anaccurage cut line cannot be produced.

SUMMARY OF THE INVENTION It is an object of this invention to solve theabove described problem by providing a knife whose cutting edge tip canbe moved positively in close contact with a ruler edge even by anunskilled person without cutting into the ruler edge.

According to this invention, briefly summarized, there is provided aknife having a handle to be manually held for using the knife and aknife blade unitarily held by the handle and having a cutting edge witha tip part and a sliding flank face near the tip part for sliding alongand being guided by a ruler edge thereby to enable the tip part toadvance in a controlled path in cutting a material lying below the ruleredge, and being characterized by a guide member unitarily secured to thehandle at a position spaced apart from and in front of the tip part inthe controlled path of cutting advance thereof, this guide member havinga sliding part for slidabl y contacting the surface of the material tobe cut and a sliding face adapted for sliding along the same ruler edgeand lying in the same plane as the sliding flank face of the blade,whereby the cutting edge is prevented from cutting into the ruler edgeduring cutting of the material by the tip part.

The nature, utility, and unique features of this invention will be moreclearly apparent from the following detailed description with respect topreferred embodiments' of the invention when read in conjunction withthe accompanying drawings, throughout which like parts are designated bylike reference numerals.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is a side elevation showing one example of a knife according tothis invention in operational attitude;

FIG. 2 is a view orthogonal to that of FIG. 1 as viewed in the directionof arrow 11 therein;

FIG. 3 is a side elevation, with a part cut away, showing the working orforward end of a second example of a knife according to the invention;

FIG. 4 is a view orthogonal to that of FIG. 3 as viewed in the directionof arrow IV therein;

FIG. 5 is a side view of a third example of a knife according to theinvention;

FIG. 6 is a side view of a guide used in the knife shown in FIG. 5;

FIG. 7 is a side view of a flat sheath of the knife shown in FIG. 5;

FIG. 8 is an end view of the flat sheath shown in FIG.

FIG. 9 is a side view of a wedge used in the knife illustrated in FIG.5;

FIG. 10 is a side view of a handle part of the knife shown in-FIG. 5;

FIG. I] is an elevational view showing the manner in which a knife ofthis invention is used;

FIG. 12 is a side view, with a part cut away, showing a fourth exampleof a knife according to the invention in a state of minimum bladelength;

FIG. 13 is a longitudinal section of the knife shown in FIG. 12;

FIG. 14 is a view orthogonal to that in FIG. 12 as viewed in thedirection of arrow XIV therein;

FIG. 15 is a side view of the blade of the knife shown in FIG. 12;

FIG. 16 is an end view of the same blade as viewed in the direction ofarrow XVI in FIG. 15;

FIG. 17 is an end view of the working or forward end of the sheath ofthe knife shown in FIG. 12;

FIG. 18 is an exploded perspective view, with parts cut away, showingthe essential parts of the knife shown in FIG. 12; and

FIG. 19 is an enlarged perspective view, with parts sectioned along aplane perpendicular to the blade, showing parts at the working orforward end of the sheath shown in FIG. 17.

DETAILED DESCRIPTION The first example of the knife according to thisinvention, as shown in FIGS. 1 and 2, illustrates one example ofconstruction wherein the handle 1 An, the knife blade 1A, and the guidemember 2A are integrally formed. The second example, as shown in FIGS. 3and 4, illustrates one example of construction in which the guide member28 is fixed to a holder or sheath 3 in which the blade is adjustablyheld. The third example, as shown in FIGS. 5 through 11, illustrates oneexample of construction wherein the guide member 2C is a separatestructure. The fourth example, as shown in FIGS. 12 through 19,illustates one example of specific construction of the arrangement ofthe third example and is provided with means for progressively feedingand locking a break-off type knife blade relative to a holder, one partof which forms a guide member.

In the first example as shown in FIGS. I and 2, the knife blade IA has acutting edge 4A, in front of which is integrally formed a guide member2A. This guide member 2A is so formed that its inner flank surface 2A0for sliding contact with a ruler lies in the same plane as the reverseflank face 4Aa of the blade, which is one face of the cutting edge 4A ofthe knife blade 1A for contacting the edge of the ruler 5. The cuttingedge 4A has a cutting edge tip 4Ab, which is so formed that, when thetip 2Ab of the guide 2A is brought into contact with the upper surfaceof the material 6 to be cut (e.g., a sheet of paper), an optimum anglefor drawcutting of the order of from 30 to 60 is obtained.

The outer surface 2A0 of the guide member 2A is formed as a curvedsurface so that the thickness of the guide member 2A decreases towardthe tip 2Ab thereof.

The above described features regarding the angle of draw-cutting and thecurved nature of the outer surface 2A0 of the guide member 2A arepossessed also by the second, third, and fourth examples.

The construction of the first example, in which the knife blade 1A andthe guide member 2A, as well as a handle part lAa, are integrallyformed, is the simplest. However, each time the cutting edge 4A issharpened, the cutting angle of the cutting edge tip 4Ab relative to thematerial 6 being cut increases slightly (i.e., the cutting edge becomesmore upright). For this reason, it is necessary to design the mutualrelationship between the cutting edge tip 4Ab and the guide member 2A sothat the cutting angle at the time of fabrication is at the minimumvalue (e.g., of the order of 30).

In the second example, the guide member 28 is provided on the working orforward end of a blade holder 3 as mentioned hereinbefore. The blade 1Bheld within the holder 3 has a cutting edge 48 along and over the entirelength of one lateral edge as indicated in FIG. 3 and is divided byoblique break-off grooves into a plurality of successively disposableblade units 18,, which can be successively snapped off, beginning withthe most forward unit, when they become dull through wear. Accordingly,the cutting angle between the cutting edge tip 4Bb and the material 6being cut when the tip 28b of the guide member 28 is brought intocontact with the material 6 can always be maintained constant.Furthermore, since the blade 1B is replaceable, the holder 3 can be usedsemipermanently if it is made to have high durability and, moreover, canbe easily fabricated.

In this case, also, the surface 2B0 of the guide member 28 to contactthe ruler edge is formed to lie in the same plane as the blade reverseface 480 of the blade 28. When the blade reverse face 48a is placed inclose contact with the ruler edge 5, the contact surface 23a is alsobrought into close contact with the ruler edge 5 similarly as in thepreceding first example.

In contrast to the above described first and second examples, in whichthe guide member 2A and 2B are permanently fixed in place forward of thecutting edges 4A and 4B, the third example has a movable guide member2C, which can be moved out of the way by pushing it into a sheath to aposition where it cannot interfere with the use of the knife forpurposes other than cutting in cooperation with a ruler edge.

The structural and functional feature of this third example of the knifeof the invention will now be described in detail with reference to FIGS.5 through 10. As shown in FIG. 5, the knife blade IC has parallellateral edges lCa and lCb and has a uniform thickness over its entirelength except at the cutting edge 4C, which is oblique relative to thelateral edges lCa and lCb. The rear end of the blade 1C is in the formof an oblique rear edge ICc, which is substantially parallel to theextreme cutting edge 4Cb, and a rear end surface lCd, which isperpendicular to the lateral edges [Ca and lCb.

On one hand, as shown in FIGS. 5 and 6, the guide member 2C, which isformed from a sheet material of the same thickness as the knife blade1C, is in the form substantially of a bar with parallel lateral edges2Cc and 2Cd, a working end tip 2Cb, and a lug 2Ce projecting out fromthe lateral side 2Cc at the other end.

In the assembly of this knife, the knife blade 1C and the guide member2C are inserted, with the lateral edge lCb of the former in intimatecontact with the lateral edge 2Cc of the latter, into a flat sheath 7 asshown in FIGS. 5, 7, and 8 in a manner such that the lateral side lCa ofthe blade is pressed in close contact with an inner edge wall on onelateral side of the sheath. Then, into a non-parallel gap formed betweenthe other inner edge wall 7b, which is not parallel to the firstmentioned inner edge wall 70, and the lateral side edge Cd of the guidemember 2C, a wedge 8 as shown in FIGS. 5 and 9 is inserted underpressure from the larger open end of the gap nearest the tip 2Cb of theguide member 2C thereby to fix the blade 1C and the guide member 2Cwithin the sheath 7.

By drawing out the wedge 8, moving the guide member 2C deeper into thesheath 7, and then inserting again the wedge 8 under pressure, the guidemember 2C can be moved out of the way from its position forward of thecutting edge 4C.

The wedge 8 having the above described function is formed from a sheetmaterial of the same thickness as the knife blade 1C and the guidemember 2C and has a shape such that its lateral edges and 8b canintimately contact the side edge 2Cd of the guide member 2C and the sideedge wall 7b of the sheath 7, respectively.

For further facility in gripping the knife, an extension handle 9 isfitted into the rear end of the sheath 7. As shown in FIGS. 5 and 10,this handle 9 at its forward end has an inclined edge for contacting therear end edge lCc of the knife blade 1C and a contact shoulder 9b forengaging the rear end surface lCd of the blade. The contact shoulder 9bforms the front part of a lug 9e having a lateral side edge 9d forsliding contact with the lateral side edge 2Cc of the guide member 2Cand a contact shoulder 90 for engaging the lug 2Ce. A cutout recess 9fis formed between the contact shoulder 9c and the rear part 9g of thehandle 9, which has straight lateral side edges 9h and 91' and for themost part extends out of the sheath 7. The side edges 9h and 91' are notparallel and coincide with the edge walls 7 a and 7b when the forwardpart of the handle 9 is fitted into the sheath 7.

In the assembly of the above described various parts to form the knifeof this third example, the rear part 93 of the handle 9 is firstinserted into the sheath 7 through the larger end opening thereof (i.e.,the forward end or lower end as viewed in FIGS. 5 and 7), and

the lug 202 of the guide member 2C is engaged with the cutout recess 9fof the handle 9 and thus left. Next, the knife blade 1C is placed sothat its lateral edge IQ) is in lengthwise contact against the lateraledge ZCc of the guide member 2C, and so that, at the same time, its rearend edge lCc abuts against the inclined end edge 9a of the handle 9thereby to assemble the knife blade 1C. The wedge 8 is then insertedinto the sheath to fix the knife blade 1C, the guide member 2C, and thehandle 9 in place relative to each other and to the sheath 7.

The relative positional relationship between the working tip 2Cb and thelug 2Ce of the guide member 2C is so determined that the tip 2Cb is inits proper position relative to the knife blade 1C with the lug ZCe inengaged contact with the shoulder 90 of the handle 9, that is, thecutting angle between the tip part of the cutting edge 4Cb and the uppersurface of the material 6 being cut becomes the aforementioned specificangle (e.g., of the order of from 30 to 60) when the tip 2Cb is placedagainst the upper surface of the material 6 with a flank face 2Ca forsliding contact with the ruler edge placed firmly against the ruleredge, and, at the same time, the reverse face IQ: of the knife blade 1Cis placed closely against the same ruler edge to carry out cutting ofthe material 6.

The operational features during use of the knife of this invention ofthe above described structure will now be described with reference toFIG. 11. The reference numerals used in FIG. 11 are those of the firstexample illustrated in FIGS. 1 and 2, but by substituting subscripts B,C, or D for the subscript A in these reference numerals, the followingdescription is rendered applicable to the second, third, or fourthexample.

First, a ruler 5 is placed in a desired position on the upper surface ofa material 6 to be cut. Then the reverse face 4Aa of the cutting edge 4Aof the knife blade 1A and the face 2Aa of the guide member 2A forsliding contact with ruler edge are pressed firmly against the ruleredge, and, at the same time, the cutting edge tip 4Ab and the workingtip 2Ab of the guide member 2A are pressed against the upper surface ofthe material 6. Then, with the knife maintained in the above describedstate, it is moved in the cutting direction.

As a result, a large resultant force of the vertical downward forceapplied to the knife blade 1A and the horizontal force applied againstthe edge of the ruler 5 acts to force the cutting edge tip 4Ab againstthe material 6 positioned immediately below the ruler edge toward thelower surface of the material, whereby accurate cutting thereof alongthe ruler edge is carried out. Since the reverse face 4Aa of the bladeand the ruler contacting face 2Aa of the guide member lie in one and thesame plane there is no possibility whatsoever of the cutting edge tip4Ab cutting into the ruler edge.

The fourth example as illustrated in FIGS. 12 through 19 is an exampleof specific practical construction of a knife in which the knife bladeis divided by oblique break-off grooves into a plurality of blade units,which can be successively snapped off when they become dull throughwear, similarly as in the preceding second example illustrated in FIGS.3 and 4. Another feature of this example is that there are providedmeans of simple construction whereby the knife blade can be fedprogressively toward the forward end of the holder in which it canslide, locked in any desired position, and retracted into and locked inthe holder when the knife is not being used.

As shown in FIG. 15, the knife blade ID of this knife has asingle-beveled cutting edge 4D formed along the entire length of onelateral edge and is divided by oblique break-off grooves S into a numberof blade units lDl, which can be successively snapped off, beginningwith the fore-most blade unit, when they become dull through wear.

This knife blade 1D is inserted into and slidably held in thelongitudinal direction by a flat sheath-like holder 3 of rectangularcross section, which has a longitudinal slit 10 as shown in FIGS. 12 and18. Near the forward end of this holder 3, one edge of the slit 10 istransversely extended in a manner to close the slit l0, and thetransverse extension 11 thus formed has a part at the forward end of theholder which is formed with a tongue-like member 12 separated from thetwo edges of the slit 10 and having an elastically deflectable property.

This tongue-like member 12 is folded upward and over onto itself nearthe forward end of the holder, and the part thus folded over is formedinto a lever member 13 disposed above the above mentioned transverseextension 11 and having a rear free end 13a.

As shown in FIGS. 13, 18, and 19, this lever member 13 has a downwardprojection 13b formed therein at a point substantially midway betweenthe fold-over point and the rear free end 13a. This projection 13b isnor mally in contact with the above mentioned transverse extension 11.

When the free end 13a is pressed by a finger to apply a force on thelever member 13 toward the transverse extension 11, the projection 13bbecomes a fulcrum whereby the tongue-like member 12 can be deflectedupward. The tongue-like member 12 is provided at its forward end with adownwardly directed locking projection 14 for positioning the knifeblade as described below.

The locking projection 14 is adapted to fit into and engage with any ofa large number of engagement holes 15 provided with a specific spacingin the knife blade 1D in the longitudinal direction thereof thereby tolock the knife blade against sliding movement in the longitudinaldirection relative to the holder 3. When the member 12 is deflectedupward, the locking projection 14 is extracted from the hole 15, wherebythe knife blade 1D is unlocked.

The centers of the engagement holes 15 are posi tioned on all of theaforementioned break-off grooves S and midway between these grooves onall of the blade units ID], that is, at the centers of these bladeunits. These holes 15 are of elliptical shape with major axes in thedirection of the break-off grooves S. In conformance with this shape ofthe holes, the projection 14 for engagement with these holes forpositioning and locking the blade also has a corresponding ellipticalshape.

In addition, as shown in FIGS. 12 and 18, a guide member 2D is formed toproject obliquely transversely from the working end of the holder on theside of extension of the transverse extension 1 1. This guide member 2Dhas a curved tip edge ZDb, and the reverse face thereof as viewed inFIG. 17 has a surface 2Da adapted for sliding contact with a ruler edge.This sliding contact surface ZDa lies in the same plane as the reverseface 4Da of the cutting ede 4D of the knife blade 1D inserted into theholder 3 and functions to prevent the cutting edge from cutting into theruler edge when the cutting edge 4D is advanced along the ruler edge 5in cutting action.

A slider 16 for undergoing sliding in the forward and rearwarddirections within the holder 3 comprises, as indicated in FIGS. 13 and18, a main sliding structure 16a accommodated within the holder, agrooved part 16b for engagement with the edges of the slit 10, and aslide key 16c, which can be pushed by a finger tip to move the entireslider 16. A stud projection 17 for blade feeding is fixed to the uppersurface of the forward end of the main sliding structure 160. This studprojection 17 is adapted to fit into an engagement hole 18 provided inthe knife blade 1D near the rear end thereof.

The slider 16 is inserted into place in the holder 3 through the rearopen end thereof. The height of the interior of the holder 3 from therear end to the vicinity of the part below the aforementioned transverseextension 11 is made substantially equal to the sum of the thicknessesof the main sliding structure 160 of the slider 16 and the knife blade1D. At the same time, the internal dimensions of the holder 3 from thepart of the tongue-like member 12 to the forward end are so selectedthat the blade ID will slide with as close a contact as possible withthe inner surface of the holder. In addition, the holder 3 is providedat its rear end with a closing member 19 detachably secured thereto.

Because of the above described structural arrangement of the knifeaccording to the invention, the following features are afforded. Theclosing member 19 is left detached, and the slider 16 with its studprojection 17 engagedly fitted in the engagement hole 18 of the knifeblade 1D is inserted with the blade in front of it into the holder 3. Bypressing the free end 13a of the lever member 13 downwardly at thistime, the member 12 is deflected upwardly, and the locking projection 14is lifted clear of the knife blade 1D and does not obstruct the forwardadvance of the blade.

When the forward tip of the knife blade 1D has been extended a desireddistance forward and beyond the forward end of the holder 3, the fingerpressure which has been pushing the free end 130 of the lever member 13down is removed, whereupon the lever action is terminated, and thetongue-like member 12 returns to its former state. Accordingly, bymoving the slider 16 slightly forward or rearward to cause the lockingprojection 14 to engage with the nearest engagement hole 15, the knifeblade 1D and the slider 16 are both locked to the holder 3. After theknife blade 1D and the slider have been inserted into the holder 3, therear end of the holder is closed by means of the closing member 19.

After use, the blade lD can be retracted into the holder 3 for the sakeof safety in the following manner. The free end 130 of the lever member13 is pressed down to lift the member 12 and thereby to extract thelocking projection 14 from the engagement hole 15, and the slider 16 ismoved rearward. Then, since the stud projection 17 is engaged with theengagement holes 18, the blade 1D is pulled rearward by the slider 16,and its forward tip is retracted into a safe position within the holder3.

At this time, by causing the locking projection 14 of the member 12 tofit into the nearest engagement hole of the knife blade 1D thusretracted, the blade can be safely locked and prevented from slidingout.

Then, when the knife is to be used, the free end 13a of the lever member13 is pressed down to cause the member 12 to deflect upward and thelocking projection 14 to be extracted from the engagement hole 15, andthe slider 16 is pushed forward to cause the blade tip 4D to project arequired distance beyond the forward end of the holder 3 in the samemanner as described hereinabove. The locking projection 14 is theninserted into the nearest engagement hole 15 to lock the knife blade 1Drelative to the holder 3.

Then, for cutting a material along a ruler edge, the reverse face 4Da ofthe cutting edge 4D and the sliding contact surface 2Da of the guidemember 2D are placed against the ruler edge. The cutting edge 4D thencannot cut into the ruler edge.

When the cutting edge 4D becomes dull because of wear, the blade unitID! of that cutting edge, i.e., the most forward blade unit, is snappedoff along the breakoff groove S, and the knife blade 1D is advanced byone pitch or twice the spacing of the engagement holes 15.

Thus, by merely causing the tongue-like member 12 formed by one part ofthe holder 3 to deflect, the knife blade 1D can be released from itslocked state within the holder. Also, by permitting the tongue-likemember to return to its normal state and fitting the locking projection14 for positioning into any one of the numerous engagement holes in theknife blade, the knife blade can be locked in the correspondingposition. Further more, the guide member formed at one part of theholder functions to prevent positively the cutting edge of the bladefrom cutting into the ruler edge when the knife is moved in cuttingaction along the ruler edge. Still another advantageous feature of thisknife is its simple construction with a small number of parts and itssimple and safe manipulation.

While the knife according to the present invention in any of its variousforms, as described only representatively above with respect to a fewexamples thereof, is adapted principally to cut paper and like sheetmaterials, it can be used also for cutting cords, strings, and the likebetween the cutting edge and the guide member. Another use is that ofthe guide member for making creased folding lines in sheet materials. Inaddition, the knife can also be used advantageously for trimming offflashes and edge irregularities of molded synthetic resin productswithout damaging these products.

While examples of the knife in which the blade has a single-beveled facehave been described above, it will be apparent that the knife accordingto the invention is equally effective with a blade with double-beveledfaces. In this case, the sliding surface of the guide member to contactthe ruler edge is positioned to lie in the same plane as that face ofthe knife blade which is to slidingly contact the ruler edge.

Thus, irrespective of the type of blade beveling, the cutting edge ofthe knife of the present invention is prevented from cutting into aruler edge, whereby the knife can be used even by unskilled persons tocut sheet materials accurately along a guiding edge such as a ruleredge.

What we claim is:

l. A knife comprising in combination: a hollow blade holder of tubularform provided with a longitudinal slit therealong; an elongated knifeblade slidably mounted in said blade holder and having a longitudinalcutting edge with a forward tip part and a sliding flank face providednear said tip part for sliding along a ruler edge thereby to enable thetip part to advance in a controlled path in cutting a material lyingunder the ruler edge, said knife blade being of a break-off type andhaving longitudinally equally spaced grooves disposed at a specificangle relative to the cutting edge of the blade and dividing the bladeinto a plurality of successively disposable blade units, said knifeblade being provided with engagement holes disposed at intervals alongthe length of the blade; a guide member rigidly secured to said bladeholder at a position spaced apart from and in front of said tip part insaid path of cutting advance; a manually operable slider engaging insaid slit in the blade holder for guided sliding movement along theslit, said slider being connected to said knife blade, whereby the bladecan be adjustably moved longitudinally by manually moving the slider;and knife bladle locking means for preventing said blade from movinglongitudinally relative to said blade holder, said locking meanscomprising a tongue-like member extending from said blade holderlongitudinally and forwardly and having an elastically deflectableproperty, a locking projection on the forward end of said tongue-likemember for disengageably engaging any one of said engagement holes, alever member integrally connected to said forward end of the tongue-likemember and extending rearwardly along the same, and a projection on saidlever member midway between the ends thereof and engaging with saidblade holder to function as a fulcrum for said lever member, wherebywhen the free end of the lever member is manually depressed, the forwardend of the tongue-like member is raised to disengage said lockingprojection from the hole with which it has been in engagement, thusallowing longitudinal movement of the knife blade.

2. A knife as claimed in claim 1 wherein said blade holder has atransverse extension extending from one edge of said slit to close theslit at the forward end of the blade holder and integrally supportingsaid tonguelike member.

3. A knife as claimed in claim 1 wherein said slider comprises a mainsliding structure accomodated within said blade holder, a manuallymovable slide key disposed outside the holder and joined to said mainstructure, and a pair of opposite longitudinally grooved parts providedbetween said structure and the slide key for sliding engagement withedges of said slit.

4. A knife as claimed in claim 3 wherein said main sliding structure hasa projection and said blade is provided with a further engagement holedisengageably re ceiving said projection therein, whereby said structureis joined to said blade.

1. A knife comprising in combination: a hollow blade holder of tubularform provided with a longitudinal slit therealong; an elongated knifeblade slidably mounted in said blade holder and having a longitudinalcutting edge with a forward tip part and a sliding flank face providednear said tip part for sliding along a ruler edge thereby to enable thetip part to advance in a controlled path in cutting a material lyingunder the ruler edge, said knife blade being of a break-off type andhaving longitudinally equally spaced grooves disposed at a specificangle relative to the cutting edge of the blade and dividing the bladeinto a plurality of successively disposable blade units, said knifeblade being provided with engagement holes disposed at intervals alongthe length of the blade; a guide member rigidly secured to said bladeholder at a position spaced apart from and in front of said tip part insaid path of cutting advance; a manually operable slider engaging insaid slit in the blade holder for guided sliding movement along theslit, said slider being connected to said knife blade, whereby the bladecan be adjustably moved longitudinally by manually moving the slider;and knife bladle locking means for preventing said blade from movinglongitudinally relative to said blade holder, said locking meanscomprising a tongue-like member extending from said blade holderlongitudinally and forwardly and having an elastically deflectableproperty, a locking projection on the forward end of said tongue-likemember for disengageably engaging any one of said engagement holes, alever member integrally connected to said forward end of the tongue-likemember and extending rearwardly along the same, and a projection on saidlever member midway between the ends thereof and engaging with saidblade holder to function as a fulcrum for said lever member, wherebywhen the free end of the lever member is manually depressed, the forwardend of the tongue-like member is raised to disengage said lockingprojection from the hole with which it has been in engagement, thusallowing longitudinal movement of the knife blade.
 2. A knife as claimedin claim 1 wherein said blade holder has a transverse extensionextending from one edge of said slit to close the slit at the forwardend of the blade holder and integrally supporting said tongue-likemember.
 3. A knife as claimed in claim 1 wherein said slider comprises amain sliding structure accomodated within said blade holder, a manuallymovable slide key disposed outside the holder and joined to said mainstructure, and a pair of opposite longitudinally grooved parts providedbetween said structure and the slide key for sliding engagement withedges of said slit.
 4. A knife as claimed in claim 3 wherein said mainsliding structure has a projection and said blade is provided with afurther engagement hole disengageably receiving said projection therEin,whereby said structure is joined to said blade.